As demand for a mobile communication service rapidly increases, a next generation mobile communication system requires efficient use of limited frequency resources and high data transmission rate.
A relay has an advantage that the relay increases coverage through removing a shadow area with inexpensive cost compared with a base station, and improves a data throughput, thereby drawing attention as one of the main technology for the next generation mobile communication system.
Generally, the relay is operated in a time division mode to eliminate interference that may occur between a base station-relay link and the relay-terminal link. Accordingly, periodic discontinuance of transmission may occur in a network system including the relay, and thus, transmission delay caused by the use of the relay may occur. Also, to eliminate interference that may occur between the base station-relay link and a direct-transmission link between the base station and a terminal, separate resources for respective links are allocated to each link and data is transmitted. Accordingly, an amount of the resource that the base station is allocated for direct-transmission users may decrease, thereby decreasing spectrum efficiency. Advantages that may be obtained from using the relay may be limited due to the above mentioned problems.
Wireless World Initiative New Radio (WINNER) which is a big European project for developing a next generation mobile communication system has been researching a relay as the core technology for the next generation mobile communication system that may cut cost and provide flexibility in deployment.
Through a result of the research to date, it is recognized that a cell coverage increases by 20% to 60% in a cellular system using the relay. Particularly, WINNER researches a cost efficiency of using of the relay, a resource management method for using the relay, and a relay deployment. From among those subjects, the resource management method for using the relay is enthusiastically researched. As an example WINNER intends to solve the problems caused by operation in the time division mode and separate resource allocation for base station-relay link transmission, using a wireless resource management method.
Recently, a relay transmission method based on superposition coding has been suggested. In a conventional method, a base station performs superposition of two different signals using time division and simultaneously transmits the superpositioned signals, and a relay that receives the superpositioned signals relay-transmits a signal which low power is allocated from among the superpositioned signals. In this instance, the base station allocates appropriate power to the two different signals according to a grade based on a signal to ratio (SNR) of the base station-relay link and SNR of the base station-terminal link, and performs superposition of two different signals to transmit. Subsequently, a terminal having a relatively insufficient channel may have difficulty in detecting signals from the received signals. In this instance, the terminal stores the received signals. However, a relay having a relatively good channel may detect all the two different signals. After detecting all the two different signals, the relay performs encoding of the signal to which low power is allocated from among the two signals considering the SNR of the relay-terminal link to transmit the encoded signal to the terminal. In this instance, the terminal may detect the signal received from the relay and eliminate the detected signal from the signals received from the base station, thereby detecting the other signal (the signal to which high power is allocated). Accordingly, since the terminal simultaneously receives two signals, frequency efficiency increases. However, conventional superposition coding may perform superposition of data transmitted over the same transmission link and transmit the superpositioned data in downlink transmission or uplink transmission. That is, the relay and the terminal may perform superposition data between the base station-relay link and the base station-terminal link to transmit the superposed data to the base station in uplink, in the same way as the base station performs superposition of data between the base station-relay link and the base station-terminal link to transmit the superposed data in downlink. That is, the relay may perform uplink transmission of data via the base station-relay link, and the terminal may perform uplink transmission of data via the base station-terminal link. In this instance, the uplink transmission of the relay and the terminal may be performed using the same resource. The downlink and/or uplink transmission of the superposition coding is disclosed in pages 31 to 33 of PCT/WO2004/075470 titled “Controlled Superposition coding in Multi-user Communication Systems”. Also, in a communication network using the superposition coding transmission, a communication entity allocates power for each user terminal to satisfy requirements of each user terminal and performs superposition coding transmission of data.
Since a conventional relay transmission method using the superposition coding is operated in the time division mode, relay-terminal link transmission should be performed after transmission of the base station-relay link. Accordingly, the periodic discontinuance of the transmission is unavoidable, and thus transmission delay may occur.
In the present specification, a relay network system that enables continuous transmission without time division and each entity for the system are disclosed.